The Stovebolt Site Forums The Shop Area Engine Shop Have my cylinders been honed too big????

Acording to th manual for my 235 piston-cylinder fit must be checked with a .0015 feeler gage inserted with the piston inverted placed half way up the piston pin flush with the block. Pulling the feeler gage should register between a 7 to 18 lb pull with a fish scale.

Mine registered 1 to 2 lbs. I tried a couple of pistons with a couple of cylinders with the same results so I'm getting a little worried. Did the machinist over hone? Can this be fixed? The block was bored .030 0ver

Rick

You should be OK I would be concerned at 18 lbs.

Although the service recommends the feeler gauge method, it isn't very accurate. Do you have new pistons? If they are used I would use a spring caliper and take measurements near the top of the piston and near the bottom, both parallel and perpendicular to the wrist pin. Or take it to the machinist and let him put a bore gauge in the cylinders. Honing usually does not remove much metal.

Are you using the 12" long feeler gauge stock like we did back in the dark ages? The last time I tried to buy some of those feelers, nobody was stocking them anymore, and most of the younger counter guys at the parts stores didn't even know what I was talking about.

Most machine shops used to hone a piston fit of one thousandth per inch of bore size, so a 3 1/2" bore piston would have a .0035" skirt clearance. That's a litle loose, in my opinion, but I've built a lot of 4" bore 350's with .0025"-.003" skirt clearance and had no problems with piston slap or excessive oil consumption. Modern hypereutectic cast pistons can be fitted much tighter that those specifications, but a couple of thousandths or slightly more skirt clearance doesn't spell disaster.
Jerry